Meteors Do Not Break Exogenous Organic Molecules into High Yields of Diatomics

Abstract

Meteoroids that dominate the Earth's extraterrestrial mass influx (50-300 microm size range) may have contributed a unique blend of exogenous organic molecules at the time of the origin of life. Such meteoroids are so large that most of their mass is ablated in the Earth's atmosphere. In the process, organic molecules are decomposed and chemically altered to molecules differently from those delivered to the Earth's surface by smaller (<50 microm) micrometeorites and larger (>10 cm) meteorites. The question addressed here is whether the organic matter in these meteoroids is fully decomposed into atoms or diatomic compounds during ablation. If not, then the ablation products made available for prebiotic organic chemistry, and perhaps early biology, might have retained some memory of their astrophysical nature. To test this hypothesis we searched for CN emission in meteor spectra in an airborne experiment during the 2001 Leonid meteor storm. We found that the meteor's light-emitting air plasma, which included products of meteor ablation, contained less than 1 CN molecule for every 30 meteoric iron atoms. This contrasts sharply with the nitrogen/iron ratio of 1:1.2 in the solid matter of comet 1P/Halley. Unless the nitrogen content or the abundance of complex organic matter in the Leonid parent body, comet 55P/Tempel-Tuttle, differs from that in comet 1P/Halley, it appears that very little of that organic nitrogen decomposes into CN molecules during meteor ablation in the rarefied flow conditions that characterize the atmospheric entry of meteoroids approximately 50 microm-10 cm in size. We propose that the organics of such meteoroids survive instead as larger compounds.

Hydrogen Emission in Meteors as a Potential Marker for the Exogenous Delivery of Organics and Water

“…Cooled CCD cameras are about 5 magnitudes more sensitive than photographic plates. The instrumental layout and response functions of our two-stage thermoelectrically cooled slit-less CCD spectrograph is discussed elsewhere in this issue (Jenniskens et al, 2004a). By purposely limiting the spectral range to about 100 nm over the 1,024 3 1,024 pixel CCD range, a spectral resolution is obtained of Dl 5 0.54 nm in first order, which is similar to, or better than, that of traditional photographic slit-less spectrographs.…”

“…Lines were identified by calibrating the vacuum wavelength of the sodium doublet to the theoretical wavelength scale (Jenniskens et al, 2004a). Any Doppler shift from residual meteor motion is negligibly small and systematic.…”

“…Elsewhere in this issue we focused on the search for the CN radical, a small diatomic organic breakup product, and found much less CN than expected if the meteoric organic matter is efficiently decomposed (Jenniskens et al, 2004a). If, on the other hand, the organic matter is carbonized by a loss of functional groups such as -OH and -H (Jenniskens and Stenbaek-Nielsen, 2004), then CN radicals would be rare but hydrogen atoms might be detected.…”

“…Meteors represent a unique chemical pathway towards prebiotic compounds on the early Earth (Jenniskens et al, 2000a(Jenniskens et al, , 2004a. Other pathways from cometary and asteroidal organics to prebiotic compounds include giant impacts during the final stages of planet accretion, and the steady rain of interplanetary dust particles and micro-meteorites that survived passage through Earth's atmosphere (Oró, 1961;Sagan, 1992, 1997;Delsemme, 1992;Brack, 1999;Maurette et al, 2000).…”

Spectroscopic anatomy of a meteor with the very large telescope (ESO)

“…An upper limit to the total carbon atom abundance in the air plasma is calculated following Jenniskens et al (2004d). Especially the region from 906 to 910 nm offers little interference from the sky airglow background.…”